Measurement Of Vacuum Quantum Noise At Low Frequencies

Vacuum fluctuation,the standard quantum limit(SQL),is very important in quantum optics.The SQL is often used as a standard reference and the precision measurement of SQL qualifies the quality of the quantum light source.Measuring SQL is even important in many research fields,such as the ultra-weak magnetic field measurement,the gravitational wave detection,and the research of quantum metrology,etc.Since the generation of squeezed light in 1985,most of the squeezed light have been generated and measured at radio frequencies(RF)at MHz and in this range the technical noise is relatively low.We don't have to stabilize and control the audio noises and we also don't need to care much about the interferences from a variety of electronic and mechanical noises.However in the gravitational wave detection or the ultra-weak magnetic field measurement,the detection frequency band is usually below kHz,even as low as mHz.It is really a challenge for traditional detectors in such low frequency range.One needs a very high classical noise suppression as the measurement time is long.In order to measure the squeezed light at low frequencies,the standard vacuum noise must be measured and calibrated first.In this thesis,a low-frequency quantum vacuum noise detection system is reported.By utilizing a self-subtraction self-designed balanced homodyne scheme,the standard vacuum noise in the regime of about 80 Hz to 400 kHz has been detected.The linearity of the vacuum noise power has been validated by varying the local oscillator power which shows that the saturated light power is about 3.2 mW.When the input local power is 400 ?W at 852 nm,the vacuum noise is about 11 dB above the electronic noise level.In the regime of about 80 Hz to 400 kHz,the standard noise power is proportional to the incident light power.However,when at lower frequencies,such as 50 Hz,the measured noise power is not proportional to the incident light power because of some non-stationary and some excess noises.The common mode rejection ratio in the test frequency regime is more than 40 dB and the maximum is 63 dB.The average common mode rejection ratio is 55 dB which means a high suppression of the technical laser noise.This low frequency vacuum noise detector can be widely used for precision measurement in quantum optics and quantum metrology.